Light Emitting Diodes (LEDs) are increasingly being adopted as general illumination lighting sources due to their high energy efficiency and long service life relative to traditional sources of light such as incandescent, fluorescent and halogen. Each generation of LEDs are providing improvements in energy efficiency and cost per lumen, thus allowing for lighting manufacturers to produce LED light fixtures at increasingly cost competitive prices. These reduced costs are expanding the applications of LED lighting from niche markets, such as outdoor street lighting, Christmas lights and flashlights, to general illumination within offices, retail, industrial, and residential environments. Within these environments, users typically want an LED light fixture to operate in substantially the same manner as their current lighting solution with at least a similar set of functionality.
Within many applications for lighting, users desire the ability to adjust the intensity of a light fixture. Changes in intensity may be desired for a large number of reasons including to create a particular mood, to reduce energy, to adjust for other sources of light (ex. ambient sunlight), to reduce glare on objects (ex. televisions) or for another lighting effect. For incandescent lighting solutions, the most common control device for controlling the intensity of a light fixture is a dimmer that contains electrical circuits including a TRIAC and/or DIAC, the dimmer typically being called a TRIAC dimmer. One skilled in the art would understand that a TRIAC dimmer is typically implemented in series within the AC power line and cuts off portions of the AC power sine wave based on the setting of a potentiometer. The modified AC signal powers the incandescent light fixture at a lower power level than a full AC signal would have otherwise, thus lower lumens are projected from the light fixture.
LED light fixtures that initially were on the market could not operate with traditional TRIAC dimmers. Instead, custom dimming controllers were developed to interoperate with LED light fixtures to control a pulse width modulated (PWM) signal that could be used to adjust the intensity of the LEDs. A key problem is these custom dimmers can be considerably more expensive than standard TRIAC dimmers. This increase in cost is due to the incredible economies of scale that currently benefit TRIAC dimmers.
To overcome this cost dilemma and to reuse the TRIAC dimmer products and form factors that are currently on the market, a number of solutions have been developed to use standard TRIAC dimmers with LED lighting fixtures. For example, National Semiconductor of Santa Clara, Calif., U.S.A. has developed a TRIAC dimmable offline LED driver LM3445 which can be implemented within a constant current architecture to illuminate high power LEDs. This component includes a TRIAC dim decoder which can interpret the setting on the TRIAC dimmer and enable it to control the output current to the LEDs.
One problem with these solutions is related to the fundamental operation of the standard TRIAC dimmers. A TRIAC dimmer in operation generates a modified sinusoid in which portions of the waveform have been cut-off (or zeroed). When rectified within an AC/DC converter, the resulting DC power level requires additional components to ensure a constant voltage level is applied to the resulting LEDs. These additional components add inefficiencies to the system. Further, the TRIAC within the dimmer requires a holding current throughout the AC line cycle in order to operate properly. To maintain this holding current, additional resistors are required to create a load for the TRIAC. This load wastes power and reduces the efficiency of the overall light fixture.
Another problem with the current implementations of TRIAC dimmers as they relate to control of LED light fixtures is that these architectures are limited to controlling the intensity of the light fixture. Since the use of the TRIAC dimmer, as currently developed, reduces the power applied to the light fixture, the current TRIAC dimmer solutions do not operate well when the information being conveyed with the TRIAC dimmer is not intensity information but information related to another aspect of the light fixture, such as color or color temperature.
Additionally, certain lighting systems, including lighting systems employing LEDs, that are currently available have control systems that are designed to work with a 0-10V dimmer. It would be desirable to provide a control apparatus that may be used with a TRIAC dimmer to provide a variable voltage control signal so that control systems of this nature may be readily adapted for use with TRIAC dimmers.
Against this background, there is a need for solutions that will better control LEDs within a lighting apparatus in order to adjust aspects, such as intensity, color and/or color temperature, of the light output. Further, solutions that re-use existing lighting control interfaces can reduce the cost of new solutions.